The potential use of polyethylene glycols of different molecular weights is being estimated in the isolated perfused liver that was developed last year. The metabolism of 3-beta-hydroxy-5-cholenoate is under study in man. Lithocholic acid has been identified as one of the metabolites. Deuterated 26-hydroxycholesterol has been prepared and shown to be metabolized to chenodeoxycholic acid in the rat. Therefore, in regard to its metabolism, no isotope effect exists and we can now proceed to the study of bile acid synthesis in neonates.